This study examines the direct and interactive effects of auditor quality on the relationship between business strategy and productivity in audit firms. Empirical data are from the 1989-2010 Survey Report of Audit Firms in Taiwan. This paper extracted auditor quality by principal component analysis. In terms of business strategy audit firms adopt, this study divides total samples into two strategy typology, defender and prospector type firms. Empirical results demonstrate that the effect of auditor quality on productivity is significantly positive. Furthermore, productivity is improved by the interaction between auditor quality and strategy, indicating that moderating effects of auditor quality on strategy and productivity.